1. Field of the Invention
The present invention relates to radiant tube burners and more particularly to recuperative radiant tube burners which utilize vitiation to reduce NOX emissions.
2. Description of the Prior Art
The need to minimize the formation of oxides of nitrogen during combustion has become a requirement of many applications of fire heaters, boilers, oil field steamers, and the like. That requirement also applies to heat treating furnaces and other applications which utilize radiant tube burners as the process heat source.
It is known that there are two basic sources of NOX formation, mainly from the nitrogen in the air and further from fuel bound nitrogen. The probable use of newly available synfuels which contain large amounts of combined nitrogen as well as the increase in the need to conserve energy further increases the demand for low NOX emissions.
Various forms of staged combustion and lower flame temperatures have been employed with conventional burners to reduce NOX emissions. Moreover, various forms of apparatus have been utilized to vitiate combustion air with products of combustion to lower flame temperature. One such apparatus is disclosed in Japanese laid-open patent application number 52-44805 wherein a portion of products of combustion flowing in an exhaust leg are caused to be mixed outside the furnace with the combustion air being provided to the burner. Another such apparatus is illustrated in Japanese laid-open patent application number 56-12904 wherein a recuperator is positioned in a stream of products of combustion. Combustion air is directed inside the recuperator to be heated by heat transferred to the tube by the products of combustion. The heated air is then mixed outside the furnace with a portion of the products of combustion. The mixture is then provided to the burner leg for combustion.
There remains a need for a radiant tube burner assembly which efficiently reduces NOX emissions.